The activated sludge method is employed widely today for the purification of wastewater. The activated sludge method is a biochemical treatment and oxidation process which employs microorganisms and oxygen to immobilize organic pollutant substances which are dissolved in wastewater into activated sludge utilizing the reproductive function of the sludge, and then utilizes the digestive function of the sludge to break down a portion of the organic pollutants into water (H2O) and carbon dioxide gas (CO2) for removal.
The typical activated sludge wastewater treatment techniques have over a century of history and many challenges are associated with such traditional techniques. For instance, the biochemical cleansing of organic pollutant substances depends largely on the quantity of microorganisms (return sludge), the density of the microorganisms, and the degree of their activity. However, to increase the quantity of microorganisms, their density, and their activity, increasing the supply of dissolved oxygen, which is essential to the microorganisms, is necessary. Without adequate supply of dissolved oxygen, the wastewater treatment may not be effective.
When the activated sludge method is employed under natural environmental conditions, namely, at 20° C. under standard pressure, 1DO (mg/L) of dissolved oxygen is required to purify 1 BOD (biochemical oxygen demand in mg/L) of organic pollutants in a five-day period. Similarly, 1DO (mg/L) of dissolved oxygen is required to purify 1COD (chemical oxygen demand in mg/L) of organic pollutants at 20° C. under standard pressure in a 30-minute to two-hour period. Therefore, under standard environmental conditions, the purification processing performance of the standard activated sludge method does not exceed 1BOD per 1DO, and in the same way, 1DO is required to purify 1COD. In other words, to purify either 1BOD of pollutant or 1COD of pollutant, 1DO of dissolved oxygen is required. As for the time required, 1BOD of pollutant require five days and 1COD of pollutant requires 30 minutes to two hours.
While many enhancements and improvements have been proposed to traditional activated sludge-based wastewater treatment, most of them presume conditions which exist naturally in the environment. To date, no innovative technology or method that brings about a revolutionary improvement in performance has been proposed.
The activated sludge method employs microbes and oxygen to effect a biochemical treatment and oxidation, isolating organic pollutants in the wastewater in the form of activated sludge, so that a portion the organic pollutants can be broken down to water (H2O) and carbon dioxide gas (CO2) for removal. For this reason, the biochemical purification of the organic pollutants depends greatly upon the quantity of return sludge (microbe flora), the density of the microbe flora, and the degree to which the microbe flora is activated.
One enhancement to traditional activated sludge-based wastewater treatment is known as “preliminary aeration.” When preliminary aeration is used, the return sludge is aerated in advance, and the return sludge (microbe flora) thus activated is supplied to an aeration vessel. However, the capacity enhancement from preliminary aeration is limited to about 30%, and due to this low improvement ratio the cost of aeration is immense. The additional cost of aeration is roughly 100%, so for a 30% improvement in performance the cost is doubled, which is clearly not cost-effective.
Similarly, another technique used today is long-term continuous aeration bubbling technology, in which the wastewater to be purified and a return activated sludge are combined in an aeration basin into a mixed liquor. Air is provided through a blower into the aeration basin. Bubbles of about 1 mm are produced, aerating the mixed liquor so that the air is dissolved into the wastewater, providing oxygen for aerobic microorganisms and activating them so they can break down organic solids in the wastewater more efficiently. However, as oxygen is not easily soluble, even with the bubbling, the achieved concentration of dissolved oxygen is not high enough to bring about a large increase in microorganisms, generally being 2-4 mg/l, a level similar to what is observed in nature, such as in rivers and lakes. While a greater number of microorganisms can be provided by increasing the amount of return sludge inserted into the aeration basin, to be effective, the increase would have to be accompanied by increasing the supply of available oxygen, which may not be possible without physically changing the existing setup. Further, currently any changes to the existing set-up, including the size and production capacity of any source of oxygen, would likely involve guesswork as to what changes would be sufficient to provide the required oxygen, with no precise relationship between the amount of oxygen provided and the amount of contaminants removed being known.
Likewise, U.S. Pat. No. 7,105,092, issued Sep. 12, 2006, to Kousuke Chiba (“'092 patent”), the disclosure of which is incorporated by reference, discloses a sewage treatment process by which activated-sludge method comprising line atomizing treatment. Wastewater is introduced into the treatment line. The wastewater passes through the adjustment vessel and the sedimentation vessel where inorganic pollutant substances are removed. Subsequently, the wastewater enters the anaerobic reaction vessel where the wastewater is acted upon by anaerobic microorganisms. Subsequently, the wastewater enters the aerobic reactive vessel where organic matter within the wastewater is converted into activated sludge by the action of aerobic microorganisms. After the conversion process in the aerobic reaction vessel, the treated wastewater solution which has had the dissolved organic matter converted into activated sludge is sent together with the activated sludge to the sludge sedimentation vessel, and the supernatant water is expelled from the wastewater treatment system. The supernatant water may also be subjected to advanced treatment for further purification.
The '092 patent further discloses that a portion of the activated sludge which has settled in the sludge sedimentation vessel passes through the sludge intake pipe and is supplied respectively as return sludge to the adjustment vessel, sedimentation vessel, anaerobic reactive vessel, aerobic reactive vessel, and sludge sedimentation vessel to effect multiple functionality for each of those vessels, and to enhance the treatment capacity of the wastewater system while allowing the remainder of the activated sludge to undergo separate treatment as excess sludge. However, each vessel has an original function and role, and in many cases, adding activated return sludge which holds large quantities of reactive gases (oxygen or oxygen with trace amounts of ozone) may interfere with those functions or roles, thus decreasing the effectiveness of wastewater treatment.
Further, the cleansing of wastewater depends fundamentally on the activity of microorganisms (activated sludge), and is thus saddled with the problem of the formation of excess sludge due to the excessive reproduction of these microorganisms, and technology to control this excess has not yet adequately been realized. In other words, the microorganisms which are involved in the cleansing of wastewater are constantly reproducing themselves and then perishing due to self-oxidization, hence controlling and managing the amount of sludge produced and the amount destroyed is extremely difficult, and the lack of this control and management is considered the critical problem of the activated sludge method. As a result, the large quantities of excess sludge that form are concentrated, transported and incinerated or buried in landfills, causing massive processing costs for the removal of excess sludge and emissions problems from the release of carbon dioxide during incineration.
In the activated sludge method, the activated sludge, that is, the microbe flora, which purifies the organic pollutants in the wastewater, can be considered to be purifying primarily through the following functions: the reproductive function, where the microbe flora absorbs organic matter as food, the flora grows and multiplies, and the organic matter is isolated in the form of a clump of microbes; and the digestive function, where the microbe flora absorbs organic matter as food, and digests the food to release energy which it uses to stay alive and carry out its life processes. To efficiently purify the organic matter in wastewater, there is an essential need for the sludge be activated, but under normal environmental conditions, the entire microbe flora is activated and controlling or managing the digestive and reproductive functions separately is impossible. Under normal conditions, the reproductive function is liable to increase, creating large quantities of excess sludge. To purify organic matter efficiently, bringing these two functions into balance is necessary. Accordingly, there is a need to be able to control and manage both digestive and reproductive functions separately.
In the activated sludge method, the wastewater purification capacity is fundamentally dependent upon the activity of the microbe flora (activated sludge). For this reason, while having the microbes activated is indispensable for increasing the wastewater purification capacity, wastewater purification techniques that simply activate in a directionless fashion result in excess reproduction, bringing about the problems of excess sludge which are among the most fundamental issues with the activated sludge method. Typically, the large quantities of excess sludge generated are concentrated, removed, incinerated, or buried, causing many problems such as very high disposal costs and the release of large quantities of CO2 into the environment.
However, there is a lack of technology available today that can handle these issues. Specifically, the microbe flora goes through a constant cycle of growing through reproduction but then extinction of the microbes by digestion, and the effective separate control and management of the growth and extinction of microbe flora as caused by these two functions is considered an extremely difficult problem.
Accordingly, there is a need for a way to control the purifying function of the microbe flora of activated sludge such that the purifying effect can be utilized technologically and industrially.